Hot dogs are fully cooked when you buy them so in that regard the hot dogs are okay and safe to eat right out of the package cold.
However it's best to heat the hot dogs up because the cold hot dogs could potentially have some bacteria on them that could cause food borne illnesses.
I've eaten hot dogs cold as a kid and never gotten sick from the cold hot dogs so you can eat the cold hot dogs if you want too.
Just be aware that if you do eat the cold hot dogs that you could possibly get food related illnesses because of the bacteria.
Although it's very unlikely that you would get sick from eating the cold hot dogs.